This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 199 37 495.3, filed on Aug. 7, 1999, the entire disclosure of which is incorporated herein by reference.
The invention relates to a method and an apparatus for determining the imbalance or unbalance of a rotating body that is mounted on a generally plate-shaped dynamometer element extending on a plane perpendicular to the rotation axis. The dynamometer element includes an inner mounting plate connected by webs to an outer frame, and at least one vibration transducer arranged between the plate and the frame for picking up unbalance induced vibrations of the mounting plate relative to the frame. The unbalance of the rotating body induces vibrations that can be detected separately as translational vibrations and pivotal vibrations.
German Patent Laying-Open Publication 28 47 295 discloses a balancing machine comprising a plate-shaped dynamometer element that is partially slitted or slotted in a spring-supportive manner and provided with connecting webs. The resulting structure of the dynamometer element includes an inner mounting plate comprising a mounting fixture for receiving the rotational body thereon, whereby this fixture may be embodied as a balancing spindle. The mounting plate is connected to the outer frame of the dynamometer element by respective webs arranged in the plane of the plate on both sides of the rotational axis of the rotational body. The vibrations arising during the rotation of the rotational body are transmitted by the mounting plate to vibration transformers or transducers. One of the transducers only detects or picks up the vibrational movements of the mounting plate about an axis, which correspond to the unbalance component arising as a result of an unbalance moment. On the other hand, the unbalance component arising from a single or individual force, namely a static unbalance, is detected or picked up by a further vibration transducer, of which the effective measuring direction extends parallel to the plane of the plate.
In the known apparatus, the dynamometer element is supported against a foundation, by two elastically flexible flat leaf springs as well as a further elastically flexible brace or support. The flat leaf springs for taking up and supporting forces in the direction of the rotation axis are secured to the mounting plate on both sides of the rotation axis of the rotational body, and respectively extend away from the surface of the plate at a right angle. The known apparatus includes separate elements in the form of elastically flexible supports or braces for taking up forces that are effective in the axial direct ion, such as axial thrust or weight forces for example. Such forces could influence the vibrating motions of the mounting plate and thereby correspondingly influence the accuracy of the unbalance determination in an undesirable manner.
In view of the above, it is an object of the invention to provide a rather simple and economical apparatus as well as a method for determining the unbalance of a rotational body, making it possible to achieve an unbalance measurement that is essentially free of interfering influences, and also to achieve an exact evaluation of the unbalance components respectively due to unbalance moments and static unbalances. It is a particular further object of the invention to improve especially the accuracy of determining the static unbalance component in such an unbalance measuring apparatus and method. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages, as are apparent from the present specification.
The above objects have been achieved according to the invention in an apparatus for determining the unbalance of a rotating body.
The apparatus comprises a generally plate-shaped dynamometer element that includes an inner mounting plate equipped with a mounting fixture on which the rotational body may be mounted, as well as an outer frame, and respective webs that interconnect the inner mounting plate and the outer frame. The apparatus further comprises at least one vibration transducer arranged between the mounting plate and the frame, where in this transducer is adapted to detect or pick-up the unbalance induced vibrations of the mounting plate relative to the frame. Particularly according to the invention, the pairs of webs that support the inner mounting plate relative to the outer frame are so embodied, configured and arranged so as to support or brace the mounting plate with respect to forces that are not induced by an unbalance, while simultaneously allowing the mounting plate to oscillate or vibrate.
Throughout this specification, the term xe2x80x9cplate-shapedxe2x80x9d is intended to define a shape that generally extends along a plane, i.e. having lateral dimensions in the plane that are significantly greater than the thickness or height dimension perpendicular to the plane. The plate plane is understood to be a plane parallel to the major surface of the plate-shaped element, and particularly of the mounting plate, for example.
According to a further embodiment of the invention, the apparatus includes not only one, but two vibration transducers arranged between the mounting plate and the frame, in order to separately detect or pick-up translational vibrations of the mounting plate relative to the frame in the plane of the plate, and pivotal vibrations of the mounting plate relative to the frame in a pivoting direction about a pivot axis of the plate that extends perpendicular to the rotation axis of the rotational body.
In the apparatus according to the invention, the plate-shaped dynamometer element receives or takes up all of the forces and moments that originate or are emitted from the rotational body, so that separate or additional supports and braces for the rotational body and for the mounting plate may advantageously be omitted. In the simplest manner, by embodying the pairs of supporting webs so that they not only support the axial thrust or weight forces, but also provide the vibrational or oscillating support of the mounting plate, it is possible to achieve an apparatus with an especially compact construction and particularly a low structural height. Moreover, the inventive apparatus has an essentially symmetrical construction with respect to the stiffness distribution as well as the mass distribution, and further achieves a very exact unbalance determination due to the improved plane separation.
The generally plate-shaped dynamometer element according to the invention may be fabricated in an especially economical manner, for example as an integral sheet metal part that is burned or cut out of a sheet metal plate and then formed as necessary, or as an integral cast part. The structure of the dynamometer element according to the invention makes it possible to achieve a very small spacing distance between the center of mass of the rotor and the reference plane of the dynamometer element. Ultimately, that leads to a more exact measurement result due to the improved separation of planes. The determination of the static unbalance is achieved very accurately, since the structure is essentially symmetrical and the measuring plane of the vibration transducer lies in the plane of the plate of the dynamometer element. The embodiment of the invention with only one vibration transducer is particularly advantageous for carrying out single plane unbalance measurements, and represents the simplest inventive structure.
In a particular embodiment according to the invention, a first pair of supporting webs is arranged in the plate plane and in a plane containing or including the rotation axis and the pivot axis. In this manner, the pivot axis for the pivotal vibrations of the dynamometer element is optimally positioned. The pivot axis formed by this pair of webs lies in the plate plane so that no interfering forces or moments can influence the measurement result. This pair of webs is embodied to be flexurally stiff with respect to bending perpendicular to the plate plane, so that these webs are adapted in a simple manner to support the forces that are not induced by an unbalance, such as the weight force or the forces that arise in the axial direction or thrust direction of the rotational body, for example due to the configuration of the rotational body as a rotor including axial force generating elements such as rotor blades. For this purpose, the webs of this web pair are constructed or embodied so as to have a high polar or area moment of inertia about the transverse axis, for example as is the case for a rectangular sectional profile member or by two rods or struts that are spaced apart from each other to form a single web comprising these rods or struts.
According to another embodiment of the invention, two further pairs of webs extending parallel to each other can be provided to both sides of the first web pair forming the pivot axis. This arrangement provides a symmetrical configuration that is especially advantageous with regard to the design, the fabrication and assembly, the calibration, and the measurement accuracy. This is also true for a further detail of the invention, in which the mounting plate is embodied with a rectangular shape, and the web pairs are respectively arranged at the ends as well as in the middle of the longer sides or edges of the rectangle.
In order to arrange the vibration transducer between the mounting plate and the frame, various configurations are possible. According to one possibility, the mounting plate comprises an extension arm protruding therefrom while the frame includes a recessed portion, and the vibration transducer adapted to detect the pivoting vibration is supported and arranged between the end of the extension arm of the mounting plate and the recessed portion of the frame. This construction achieves a very compact dynamometer element that is able to carry out a very exact measurement.
The invention provides very simple measures for arranging the plate plane of the dynamometer element alternatively in the horizontal direction or the vertical direction. Thus, the inventive dynamometer element may be used in balancing machines that are adapted to special requirements, with vertical or horizontal rotation axes, in a very simple manner.
If the rotation axis is oriented in the vertical direction, whereby the plate plane extends in the horizontal plane, this advantageously provides a free space below the dynamometer element that is free and clear of separate supporting elements. Thus, the resulting free space beneath the dynamometer element can easily be used to accommodate other elements of a balancing machine or an unbalance measuring machine, for example the drive and control arrangements or clamping devices for securing the rotational body onto a balancing spindle or onto the mounting surfaces of the mounting plate. Overall, this leads to a compact, user-friendly, and service-friendly construction.
The above stated objects have further been achieved according to the invention in a method for determining the unbalance of a rotational body, using a plate-shaped dynamometer element including a mounting fixture for receiving the rotational body. According to the inventive method, the unbalance induced vibrations of portions of the dynamometer element are separately detectable or can be picked-up as translational vibrations and as pivotal vibrations. Further, particularly according to the invention, all of the forces and moments originating and emanating from the rotational body are transmitted into and through the dynamometer element. As mentioned above, this avoids the need for additional separate supports.